DRV8711 issue

Hi John

Have you tried with the GUI and the MSP430 built just for the boostpack board?

What is parameters you using now?

Best regards,

Hi John,

Can you provide the motor used (model number, inductance, resistance, current rating)?
What number of steps per second is being used at each stepping level?
Can you provide scope captures showing the behavior? Current versus step is best.

Hi Wilson,

John posted this question on my behalf. I tried using the GUI with no success. I am using the MSP430F5529LP which i believe the program should be able to use as it is an option in the GUI menu and I selected that chip when i set up the program, however the GUI suffers from a critical error that I am unable to find a solution to thus far.

Cheers,

Luke

Hi Luke,

The demo firmware/software is only compatible with the G2553 LaunchPad at the moment. That is the most likely source of this error.

www.ti.com/.../MSP-EXP430G2

Hi Rick,

John posted this question on my behalf. The motor I am using is a part of an electronic needle valve, the "datasheet" is here: 

www.clippard.com/.../Clippard%20SCPV%20Proportional%20Valve.pdf

Here is the Useful information:

I am running the Motor at 14V, their engineers said that it will work with up to 3x the voltage no problem, and I know the Booster pack needs a minimum of 8V on the VM input. 


The waveform below continuously toggles the step bit high and low waiting 8us between instructions. The step size is 1/32 Unfortunately I only have 1 current probe it is on A2. Inputs 3 and 4 are on A1 and A2. The current looks the same on any other line.

Thanks,

Luke

Hi Luke,

If I read the motor specifications correctly, the maximum speed is 590 Hz (590 full steps per second). This equates to 18880 Hz in 1/32 mode.

According to your description, the step pin is being toggled at faster than 18880 Hz. If so, the current waveform may not be able to follow the indexer table.

In general, the DRV8711 is more than you need to drive this device. You can also look at the DRV8846 or DRV8880. Both of these can drive the needle valve and have integrated FETs to reduce the system cost.

Hi Rick,

Unfortunately I lowered the time between steps to send you a better waveform. This is what it looks like over an 8ms period, which should be 4kHz on 1/32 mode and 125Hz for full step. I have also tried only sending it a step command once per second which makes a waveform like this with a 30 second period.

As you can see the steps change roughly every 220ms
This is it zoomed in. To me it doesn't look like a proper micro-stepping waveform but im not sure what the issue is.

Thanks,

Luke

Hi Luke,

There is still the MSP430G2553 that should be resolved before looking at the waveforms. Once that is resolved, please double check the waveforms.

Hi Rick,

It'll take me a few days to get the launchpad the GUI was designed for. Apparently the program wont run on an MSP430F5529LP. If you are wondering how my system is working now the answer is jumper wires, which of course i verified all the connections and ensured that I can read and write the buffers and tell it to take steps, full steps work as advertised.

Is there anything else I can try in the mean time? I read through the entire data sheet looking for things i might have missed, but setting up micro-stepping should be as easy as setting the MODE bits in the control register and enabling the motor then giving it a direction and telling it to step.

Thanks,
Luke

Hi Nick,

I have acquired two of the MSP430G2553's and I am now running into the same problem with both of them. I run into a stream of critical errors. Here are a few:

The USB cable loads the program onto the board with no issue and its not touched between that and launching the GUI so i doubt that is the problem. I've looked at the forums for a fix but the one I think you answered here: e2e.ti.com/.../1322941 is not the same problem as I am having, I am providing VM 15 V from a Power Supply.

What should I do?

Thanks,

Luke

Have you checked your Status register to see if any error flags are active?  Your images look like they could show a 4;1 microstep with the current shutting off too soon.

Now that  you have a current probe you should verify your currents at 1:1, 2:1, 4:1, etc.  Your current should be following Table 4 and Figure 16 in the datasheet.

Single stepping with a multimeter in series with the motor and set to measure current should give a better indication of what is going on. 

Do you have another DRV8711 that you can try? 

Testing with a 13 ohm resistor in place of the motor might help too. 

My status register is all zeros, though that doesn't mean that it isn't stalling seeing as I left SDTHR at default 0x40, it would just mean that there isn't enough back emf to trigger the stall flag. Although if it is stalling it is doing so in a very consistent pattern. What would I do if it was stalling and not triggering the stall flag? increase the voltage to VM?

The peak current draw for a full step is 1.7A and looks pretty good the waveform for a full step looks like this:

The peak current for a 1/32 step is 2.37A and looks like this:

I would say that you are correct in that the current is shutting off too soon. I have 3 DRV8711 boosterpacks and they all act the same, unfortunately I dont have any resistors that can handle more than 1/10W, I tried to take a scope capture for you but they caught fire before the scope could catch a transition.

Thanks,

Luke

Hi Luke,

Your description indicates that the LaunchPad was successfully programmed. This error says now that the GUI cannot communicate over UART to the MSP430.

One quick sanity check...can you verify that the UART jumpers have been rotated? This allows for the hardware UART to operate. Section 3.2 of the User's Guide.

I'm wondering if you have a disconnect with your motor manufacturer.  The motor is rated for 0.385A, so at 13 ohms that is 5VDC.  When they said you could run it at 3x that voltage they probably meant enough voltage to overcome the inductance (V=L*di/dt) at speed.  At 2.37A you are overdriving this motor by 6 times the rating!  Are you sure you haven't damaged the motor? 

0.385A^2 * 13 ohm = 2W so you are correct that you will need a large resistor (or a bunch of smaller ones). 

You can set your stall detection to external (EXSTALL = 1) so the DRV8711 won't care. 

Whether full stepping or microstepping you should see the same peak current (not 1.7A changing to 2.37A); it sounds like your register settings are not getting set to what you believe they are.  Are you accidentally toggling the PWMMODE bit? 

Single stepping is the key to debugging this.